Method of treating filaments for incandescent electric lamps



Patented July 10, 1923.

4 UNITED STATES PATENT OFFICE.

EAR-BY K. OI NEWARK, NEW JERSEY, AHSIGNOB TO WESTINGHOUSE LAX? OOKPAJIY, A CORPORATION OF PENLNBYLVANLL KETHOD OI FILLIIENTS 10B INGANDESCENT ELEGl'B-IG LAMPS.

10 Drawing.

To all whom it may concern:

Be it known that I, Ham H. Sm'rn, a citizen of the United S and a resident of Newark, in the county of see: and State of New Jersey, have invented a new and use- Impmvement in the Method of Treating Filaments for Incandescent Electric Lamps, of which the following is a specification At the presentstate of the art, it is well lmown that-a metallic filamentary material, such as'molybdenum, tungsten and similar highly refractory metals, unless treated In some manner, will tend to alter internally when raised to a point of incandescence in a lamp and that the dogma of'alteration will depend upon such factors as the size of filament, e'iliciency at which it is operated, length of service, etc. One such form of alteration is manifested in what is commonly known as sagging", the eifect of which is an elongation of the filament, particularly if of the coiled type; This effect or elongation produces a detrimental change in a lamps efliciency, resulting from increased length of the filament, and further promotes the short circuitingof at lciist ortlons of the filament, es eciallyif of t e spirally wound type, wit the-consequent early fullu re of the same.

It is an object of this invention to so treat a metallic filamentary material as to make it substantially non-sag. The treatment is given to a filamentary body in a. coherent or homogeneous state, which bod ma he formed of tungsten powder pressed Into an ingot and sintered to render it workable. The sinterin process causes the ingot to shrink and enome cohelcnt, thereby conditioning it for subsequent mechanical work i or drawing down into filamentary form.

Tt is a further object of the invention to give this treatment at such steps in the manufacture of a lamp as to practically render it impossible to destroy the structure of the filament resulting from my treatment, by subsequent operation wherein the filament may be heated to a high tcinpurntuwr.

I propose to accomplish the above nhjects by controlling the crystalline structure of a metallic filamentuous substance. I have observed that thcrc is a definite relation Application fled December 19, 1917. Serial in. coma.

between the grain structure and the saggin and non-sagging prugerties of a filament. T have further observe that by treating a tile ment, preferably composed of certain, constituents, it is possible to predetermine the crystalline structure of the filament and give it a grain structure which remains substantially fixed or is unaifected by subse ueut operations. This treatment contemp ates raising the temperature of the filament, by the application of an electric current of a given strength, to what may be termed the "germinative temperature and maintaining it at'this condition for a limited time. The germinative temperature may be defined as the minimum temperature at which two adjacent grains can coalesce to form one let 2 grain provided that. this larger grain wil have sulliciently increased its power of attack to enable it to absorb ad acent grains whichcannot coalesce with each other. The gcrminative temperature may also be con sidered as a range existing between two other ranges the preceding one being called the inert temperature range and the one following being termed the growth range.

The coalescence or grain growth, i. e., the absorption of certain grains by certain other grains, may be promoted or retarded and the germinutive temperature accordingly lowered or raised by such factors as initial grain fineness, prior plastic deformation, mobility of the grain, etc, and in practicing my invention this must be tukcn into consirlcrution in determining the treating schedule for any given size or kind of lilamcnt l have found by experimenting that the crystalline structure requisite to prevent a lilumcuL from suggil'ig, is one in which the grain structure is large, the grains being of rnnsirlcruhlc lvngth and of such a forma- [ion as to mcr-lup or interlude with each olhcr. liy over-lapping in this manner the urruugcuurnt of grains is such that they tend In support, uni-h other and this prevents a sagging of the filament. As stated-above, it is lmsxilllt to subject thu filament to a hunt Hunting schedule which will not only control. lml produce u crystuliine structure having long ou-rlnpping gra ns. It is important that this treatment he 'ven at a time before the Element is ra' to a temperature at which grain growth starts, which naturally varies with the size of the filament.

My. treating schedule me be applied to my ighly refractor mete such as tung sten, and influence he internal structure thereof, but as intimated above more satis- (mtresults m be obtained a: the sumentary material is of a certain consistency. In other words, the filamentary may be made of such a. composition as to be inherently susceptible to in treating schedule and therebyaccelerste he formation of a given grain structure when the filament is raised to its gel-initiative temper-an tux-e. Wire which is especially responsive to my treatment in producing e non-sag structure, forms the subject matter of a wing application of Dr. R. D. Hall, filed mber 1.9, 1917, Serial #207,838, and contain from 2 o to 7% by volume t) of silica and 1% to 2% by weight) with tungsten. The

may to 1% by we to .4% by volume of thoria. combin character of this wire forms no this temperature in t e case of the specie] wire referred to, is approximatel 1170 C. In carrying out my invention have discovered that best results are obtained in reducing a. non-sag crystalline structure In the special form of filamentary materiel mentioned above, by subjecting it in a reducing atmosphere to the following schedule; apply a current of the rating for which the lamp is designed, gradually increase this current until it reaches 130%.

at the end of one 'minutes time, and then maintain this latter current strength for e riod of one minute after which time it is interrupted. This schedule has been found to give very satisfactory results for all tungstcn as filled lamps above watts, but it is o vious that it IS subject to modification in treating tlifl'erent type lamps which may have different type filaments. If :1 Element which has received the treatment just de scribed is examined undw' microscope, it. will be seen to ossess n cry-aniline structure in which all grains are of largo and of a particular formation, i. e., crysu. s of conmaterial part of the present invention and further description sidere ble length which interlace with each other. When the filament is embodied in a lamp and life tested,ai: will be found to rare I. non-ea g'qu 't or to rt While I hafi t lescribe p pa y being practiced in connection with J '11 forms of filament, I wish it und that in its broadest aspect, it contemplatestheim duced formation of crystals of definite size and shape, arranged so u to form an interlfcin st-ucture with each other, and fig-231- tiat eterminin apro rtneatin ule, ibis my bclief't at so eorystnlfine for motion may be obtained in any kind of a highly refractory metallic filamentary ma- I terial.

What I claim as my invention is:

l. The method of treating a refrsctory metallic filamentary body of tungsten or equivulent metal contuinin crystal growth directing ingredients, w ich consists in heat-- treating said body accordin to a predetern-lined seasoning schedule t at will-cause lhc develop] ent of crystals having considerable lengt s'o arranged so to overlap or interlnce with cachotlier.

2. The method of treat body of tun n or equiv out metal containin auxi iary ingredients to produce a crysta ine structure therein, which renders the same resistant to sagging, which consists in heating said filamentary.- body to its germinutive tcm rature end holding it at said temperature lfl accordance with e predetermined seasoning schedule. r

8. The method of treati a filamentary body of tun ten or equiva ent metal contninin auxi iary ingredients to reduce a crystal 'ne'structure therein whi renders the same resistant to sagging which consists in treating said lilamentery'body according to a predetermined seasoning schedule before the temperature of said filamentary body is raised to-one exceeding its germinntive tempernturc.

4. The method of reducing a. non-eegglng filament from a amenta bodycomposed rimarily of tungsten so having in timnte y assocmted therewith silica ,and thoria, which consists in heet-treetin' said filamentary body in accordance wit the following seusonlug schedule assing a. current about 90% of the rating or which the lamp is designed in which said filament into be incorporated, gradually increasing said current until its value reaches about 130% at, the end of about one minute and maintaining said latter current strength for about one minute and thereafter interrupting said current.

5. The method of roducing a nomsaggring filament from uhlamentaty body composed primarily of tungsten and having iuti match" associated therewith silica and thoria, which consists in heat-treating said filamenmy invention as body in acoordanoeyith the following said latter currsnt strength for about one minute 1nd thereafter interrupting said current, said h'aat-tmtment being conducted in a reducing atmosphere.

In testimony whereof, I have hereunto subscribed my name this 3rd day of Dec.,

HARRY H. SMITH. 

